This invention relates to spinal support rod kits and methods for the treatment of spinal column shape deformation.
Support rods which are used to support a spinal column can be fastened to the patient's vertebrae by means of fastening devices such as for example by bone screws or hooks. The support rods can help to support the spine in a desired alignment. A support rod can define a shape towards which a deformed spine is to be corrected. Attaching the vertebrae to the rod causes vertebrae which are out of position to be drawn towards the rod, so that they can then be retained in a correct alignment against forces imposed by soft tissue tending to revert the configuration of the spine towards the deformed shape. Correction of the spinal deformation can involve application to the vertebrae of translational forces or of torsional forces or both, to cause vertebrae to translate and to twist or both.
A known system for the treatment of scoliosis involves a posterior approach using two sub-laminar hooks placed at the superior and inferior end vertebrae of the curve. A single rod is then inserted in the hooks and a distraction force is applied to correct the curve.
Subsequent refinements have reduced the forces which are applied to individual vertebrae and to improve the application of correction forces during extended periods after implantation.
More recent systems involve use of distraction and compression rods which are fixed to the spine with several hooks around the pedicles, transverse processes or laminae of some vertebrae, and/or screws through the pedicles of selected vertebrae. These multi-segmented double rod systems allow distraction and compression at different levels to improve alignment in the lateral and sagittal plane but nominal axial rotation. The Cotrel-Dubousset correction technique uses a rod rotation (rod to spine manoeuvre) in which a shaped rod is rotated in the concave side of the curve of the spine, and anchored using proximal and distal hooks. Spinal instrumentation which is sold by DePuy Spine Inc under the trade mark ISOLA uses vertebral translation (spine to rod manoeuvre) in which vertebrae are translated toward the rod with various specifically designed instruments and implants, for example hook and pedicle screw extensions and wires.
Application of torsional forces to neutral vertebrae can result in some imbalance and unwanted movement of those vertebrae.
It can be challenging during a surgical procedure to implant a spinal support rod to ensure that appropriate forces are applied to a rod in order to deform it, so that appropriate bending and torsional forces are then applied by the rod after implantation to the patient's vertebrae. Different such forces can be required at different points along the patient's spinal column. It can also be important to control the amount of force that is applied at each stage during the procedure to each vertebra because high localised forces can result in the patient's bone tissue being damaged.